Set up basic deterministic lockstep

src/Campaign.h

@@ -55,6 +55,10 @@ namespace FRG {
 		std::string startStatePath;
 		std::string questsPath;
 		bool tutorial = false;
+		// Existing character IDs assigned to multiplayer connections in order.
+		std::vector<std::string> networkPlayerSlots;
+		// Version token shared by clients with identical deterministic content.
+		std::string networkCompatibility;
 		// UI layout shown while the campaign loads (preloaded with the rest of the UI).
 		std::string loadingScreenPath = kDefaultLoadingScreen;